1. Field of the Invention
The present invention generally relates to devices for optically connecting the ends of waveguides such as optical fibers, and more particularly to an article which splices a plurality of pairs of such optical fibers.
2. Description of the Prior Art
Splice devices for optical fibers are known in the art, but there is still a need for a quick and reliable method of splicing a plurality of fibers in a high density environment. Prior to the introduction of splice devices which join a plurality of optical fibers in a single splice body (discussed further below), this was accomplished by utilizing a plurality of single fiber (discrete) splice devices. This approach was very time consuming, however, and further resulted in a large volume of splice bodies which crowd junction boxes, or require specialized splice trays to keep the fibers organized.
Several systems have been devised to address the problem of multiple fiber splicing. One technique, mass fusion welding, requires that each fiber be placed in a groove of a rigid substrate having several such grooves. Best fit averaging is used to align the fiber pairs and an electric arc is created, melting the fiber tips and permanently fusing them together. The primary, and very significant, limitation of fusion splicing is the great expense of the fusion welders. Fusion welding also precludes later fiber removal or repositioning.
Another common multiple splicing technique requires the use of adhesives, again with a substrate or tray that has a plurality of grooves therein. For example, in U.S. Pat. No. 4,028,162, a plurality of fibers are first aligned on a plastic substrate having fiber aligning grooves, and then a cover plate is applied over the fibers and the substrate, the cover plate having means to chemically adhere to the fiber and substrate. Adhesives are also used in the optical fiber splice devices disclosed in U.S. Pat. No. 4,029,390 and Japanese Patent Application (Kokai) No. 58-158621. The use of adhesives is generally undesirable since it adds another step to the splicing process, and may introduce contaminants to the fiber interfaces. Splice devices using adhesives also require extensive polishing of the fiber end faces to achieve acceptable light transmission, and some adhesive splices further require the use of a vacuum unit to remove trapped air.
The '390 patent represents an improvement over earlier multiple splice devices in that it utilizes a foldable holder having a series of V-grooves on both sides of a central hinge region. The method of attaching the fibers to the holder, however, presents additional problems not present in earlier splices. First of all, since adhesive is used to affix the fibers to the holder before splicing, the cleaving of the fibers becomes a critical step since the cleave length must be exact to avoid any offset of the fiber end faces, which would be extremely detrimental to splice performance. Secondly, it is critical that the opposing V-grooves be exactly aligned, which is unlikely with the hinge depicted in the '390 patent; otherwise, there will be transverse fiber offset resulting in increased signal loss. Finally, the '390 holder would not maintain the opposing plates perfectly parallel, which is necessary in order to optimize transverse alignment of the fiber pairs, and also affects fiber deformation.
Another problem with several of the foregoing splicing devices is that they used rigid substrates to clamp the fibers. There are several disadvantages to the use of rigid substrates. First of all, it is generally more difficult to form grooves in a rigid material, such as by etching, grinding or erosion, which increases manufacturing cost. Rigid substrates must also be handled more carefully since they are brittle and thus easily damaged. Most importantly, the use of a rigid substrate having grooves therein results in poor alignment of the fiber pairs (as well as unnecessary fiber deformation), leading to higher insertion loss. These problems are compounded in stacked configurations such as those shown in U.S. Pat. Nos. 3,864,018, 4,046,454 and 4,865,413.
These difficulties may be avoided by the use of a substrate which is malleable, elastomeric or ductile. Unfortunately, however, the use of such materials has not been fully appreciated nor implemented. For example, U.S. Pat. No. 4,046,454 teaches that the rigid V-grooves may be lined with a ductile material. This complicates the manufacturing process, however, and adds significant cost. In U.S. Pat. No. 4,102,561, the splice device utilizes two alignment members formed of a resilient material which may deform against the fiber surfaces. That splice, however, requires the attachment of two subassemblies prior to insertion of the fibers into the alignment members, and further uses about a dozen clamps and bolts, making the device very difficult to use in the field (similar problems apply to the device illustrated in U.S. Pat. No. 4,045,121). The primary clamping action directly at the fiber interface also causes deformation of the fiber resulting in more signal loss than if there were a more gradual clamping toward the interface. This problem also applies to other splice designs, such as that depicted in European Patent Application No. 88303777.2, which further suffers from the non-uniform application of clamping forces to different fibers.
In light of the foregoing, it would be desirable and advantageous to devise a high performance splice device for multiple optical fibers which does not require fusion welding, or adhesives and polishing. The device should provide a uniform clamping force to each of the fibers, and provide gradual clamping to minimize undesirable deformations such as microbending at the clamp transition. The cleave length of the fibers should not be critical, and means should be provided to optimize fiber alignment, including the use of malleable clamping surfaces. Finally, the splice should be simple to use, especially for field installation.